(1) Field of the Invention
This invention relates generally to infrared transmitter light-emitting diodes (LEDs) and relates more specifically to a circuit driving infrared transmitter LEDs with temperature compensation.
(2) Description of the Prior Art
The usage of infrared transmitter and receivers is getting more and more popular and is known for numerous different applications and includes a transmitter (such as an infrared light emitting diode (LED)), which transmits light in the infrared range, and an optical receiver (phototransistor or photodiode or photoresistor), which converts the optical infrared signal into a proportional electrical signal. However, the transmitter (infrared LED, for instance) and the receiver being used (phototransistor, for instance) are highly temperature-dependent in their electro-optical properties. Without suitable temperature compensation, temperature fluctuations would be interpreted as fluctuations of information transmitted and would lead to incorrect results. Furthermore a constant current through an infrared LED is mandatory to maintain a light efficiency.
It is a challenge for the designers of infrared transmitter diodes to maintain a constant current through a LED and ensure an effective temperature compensation for the infrared LED.
There are known patents or patent publications dealing with drivers for infrared LEDs
U.S. patent (U.S. Pat. No. 4,956,591 to Schierbeek et al) proposes a control for a moisture sensing assembly, adapted for mounting on the inner surface of a vehicle window or windshield to control vehicle accessories such as windshield wipers, maximizes the window area being sensed in relationship to the size of the assembly and provides immunity to interference from environmental influences. In the preferred embodiment, moisture on the outer window surface is detected by first and second moisture sensors each including infrared energy radiating diodes and radiant energy detectors which detect and process radiant energy to produce a moisture signal that is a function of the moisture on the window. A synchronizing circuit intermittently actuates the radiating diode for the two sensors individually and alternating at equally spaced intervals. The synchronizing circuit also inhibits the radiant energy detectors from processing the radiant energy signal except when the corresponding radiating diodes are emitting energy in order to prevent interference from the other radiating diodes and environmental influences. The synchronizing circuit includes a pair of oscillators, which include capacitors and coupling devices that coordinate the discharging of the capacitors in a manner that provides equal intervals between alternating output pulses from the oscillators.
U.S. patent (U.S. Pat. No. 6,781,539 to Matsui) discloses a remote control transmitter for operating an electronic appliance with an infrared ray, which is easy-to-operate and inexpensive. The remote control transmitter does not change the illumination of an illuminating device even when an operation key is manipulated. The remote control transmitter has a voltage control circuit including a diode having substantially the same power consumption as an infrared ray output means, and a control transistor connected parallel to the diode for turning on and off according to the electric signal from a microcomputer. Since a current flowing in the diode is controlled by the control transistor, a constant voltage is always applied to the driving circuit for lighting up the illuminating device regardless of a manipulation of the operation key.
U.S. patent Publication (U.S. Pat. No. 5,790,615 to Beale et al.) describes an infrared transmitter circuit causing an output current to flow to a light emission diode via a current mirror circuit constituted of three transistors by using a current supplied from a power source circuit, so that the light emission diode emits light. When a voltage V1 varied by charging a capacitor with a current flowing from the power source circuit exceeds a reference voltage (voltage V2), an output of a comparator resets a D flip-flop, so that an output of the D flip-flop varies to “0”. Thus, an output of a NAND gate to which that output and a transmission signal are inputted causes a transistor (N-channel FET) to turn ON so as to stop operation of the current mirror circuit, and causes a transistor (P-channel FET) to turn OFF so as to cut a connection between the power source circuit and a power source line. Thus, it is possible to reduce power consumption in operation of a protection circuit, which stops supplying the output current to the light emission diode.